The present invention relates to a method of preparing a fully ceramic artificial crown and a preparation kit used therefor.
In an aesthetic crown or inlay restration, a material obtained by baking a pottery material called metal-bonded porcelain onto a metal core has heretofore been used. However, this dental prosthetic material has a problem in that the gum undergoes the discoloration due to elution of metal ions. Another problem is that a metal in the core shuts off light making it difficult to reproduce transparent feeling as that of a natural tooth.
On the other hand, a fully ceramic artificial crown (also called all ceramic artificial crown) of which the core, too, is formed of ceramics does not cause the gum to be discolored by the elution of metal ions, since no metal core is used. Besides, since a material having a transparent feeling close to a natural tooth is used as the ceramic core, it is made possible to realize a natural transparent feeling and to obtain a color feeling closer to a natural tooth due to the lamination of a special porcelain. So far, a metal has in many cases been used as a core of the artificial crown from the standpoint of strength. In recent years, however, technology has been developed to use, as a core material, a crystallized glass that exhibits a large strength (Japanese Unexamined Patent Publication (Kokai) No. 36316/1998, and a fully ceramic artificial crown has been much expected.
In preparing a fully ceramic artificial crown, in general, it is accepted practice to bake various porcelains onto the ceramic core, the porcelains having different color tones for each of the portions of the crown corresponding to constituent portions of a natural tooth in order to realize appearance close to a natural tooth. Concretely speaking with reference to FIG. 1 which is a sectional view of a fully ceramic artificial crown mounted on an abutment tooth P, it is a practice to bake, in the form of layers, a body porcelain A for reproducing an ivory color, an incisal porcelain B for reproducing an incisal color, a translucent porcelain C for producing a transparent feeling and, as required, a cervical porcelain D for reproducing a color of a neck of a tooth on the ceramic core E. These porcelains are generally obtained by blending a powdery ceramic component having an average particle diameter of from about 15 to about 100 xcexcm with pigments that meet use of the porcelains.
A simple baking of the porcelains in an overlapped manner is not enough for reproducing a delicate color tone of a natural tooth or a pattern specific to an individual person. Therefore, it has been done to impart a color by using a porcelains called staining powder that contains a pigment in a relatively large amount, to smooth the surface and to impart transparency by glazing by baking a porcelain called glazing powder which does not almost contain pigment. Here, in order to realize a delicate color and a feeling of high surface quality, the ceramic component in the staining powder or in the glazing powder, usually, has an average particle diameter of from about 1 to about 15 xcexcm, which is smaller than the average particle diameter of the body porcelain and so forth on described above.
And even in these staining powders, glazing powders and the above-mentioned various porcelains porcelains as for the fully ceramic crown having coefficients of linear thermal expansion close to that of the crystallized glass used as the core material, and further having low firing temperatures and improved chemical resistances have been proposed. (Japanese Unexamined Patent Publication (Kokai) No. 139959/2000).
As the methods of producing a ceramic core used for the preparation of a fully ceramic artificial crown, there have been known a casting method in which the crystallization of the crystallized glass is performed by heat treatment after casting a molten crystallized glass into a mold, and a heated/pressurized molding method in which a crystallized glass is softened to a suitable degree without being melted and is poured into a mold to prepare a molded article.
According to the above heated/pressurized molding method, the crystallization of the crystallized glass is happened during the molding, making it possible to shorten the entire working time of molding inclusive of crystallization compared to the casting method, which is an advantage. According to this method, further, the ceramic material is slowly pored into the mold in a highly viscous state of about 102 to 106 poises without heating it nearly to its melting point, hence one can avoid involving bubbles and the reaction such as baking with the investment material (mold material) forming the mold during the molding, and one can obtain a ceramic artificial crown having stable properties (Japanese Unexamined Patent. Publication (Kokai) No. 206782/1999).
Thus, the heated/pressurized molding method exhibits excellent characteristics as a method of producing ceramic cores requiring, however, an extended periods of time for molding the core since the highly viscous material is slowly poured.
In order to shorten the molding time, there can be contrived to increase the rate of molding the crystallized glass by increasing the load at the time of exerting pressure and elevating the temperature at the time of molding.
When the load is increased by using a weight, however, the weight of a large size must be used for the pressurized molding device. Even in other pressurized devices, it is necessary to employ a structure that withstands the pressure, arousing a problem in that the device tends to become bulky. Due to a large load, further, the surface of the investment material is rubbed by the crystallized glass that is poured. Depending upon the investment material that is used, therefore, the surface of the molded article is coarsened or the mold is broken. When the temperature is raised during the pressurized molding, further, the crystallization proceeds faster, and it becomes difficult to control the crystallization and the quality of the obtained core decreases.
According to the heated/pressurized molding method as described above, a new problem arises when it is attempted to shorten the molding time by increasing the load at the time of exerting pressurize or by elevating the molding temperature. It has, therefore, been urged to provide a method of shortening the molding time without accompanied by the above-mentioned problem.
The dental porcelain favorably used as the ceramic core surely exhibits excellent properties. When it is really used, however, the color of the core ceramics tends to be seen through due probably to that light is not suitably scattered inside thereof. To obtain a color tone comparable to that of a natural tooth, therefore, it is necessary for the dental porcelain to impart a suitable degree of transparency which inhibits the underlying color from being seen through.
It is an object of the present invention to develop a method of efficiently producing a fully ceramic artificial crown of a high quality within short periods of time.
In order to overcome the above-mentioned technical assignment, the present inventors have forwarded a keen study. As a result, the inventors have discovered the fact that when a core is molded by using a mold on which surface is formed a film of a solid lubricant by a particular method, the heated crystallized glass can be poured into the mold at an increased rate causing neither the surface coarsening nor the breakage of the mold, and have thus arrived at the present invention.
That is, a first invention is concerned with a method of preparing a ceramic artificial crown by applying at least one kind of dental porcelain selected from the group consisting of a body porcelain, an incisal porcelain and a translucent porcelain onto the surface of a ceramic core molded by heating and softening a ceramic material and putting it into a mold with the application of a pressure followed by firing; wherein
said mold is the one formed by burning a wax pattern after having removed a crucible former from an assembly which comprises:
said crucible former having a pole member formed on the central portion of a cylinder with bottom, said pole member having a recessed fitting portion at a central portion in the upper surface thereof;
said wax pattern secured to said recessed fitting portion and applied with a solid lubricant on the surface thereof;
a ring with a backing layer that engages with said cylinder with bottom; and
a investment material filled and cured between said ring and a tooth-shaped model; and wherein
a portion corresponding to the pole member of the crucible former of said mold is filled with a ceramic material which is, then, pushed by a plunger to mold a ceramic core.
According to the above-mentioned preparation method of the present invention, the wax pattern can be easily secured during the process of making the mold and, besides, the mold is not broken, the surface of the molded article is not coarsened and the crystallization does not lose uniformity even when the flow rate of the ceramic material such as the crystallized glass is increased at the time of molding the ceramic core, making it possible to produce an article of a quality comparable to that of the ceramic cores obtained by the conventional heated/pressurized molding method maintaining good reproduceability. The above effect is obtained probably because when the mold is produced by a particular method as described above, an appropriate lubricating film which lowers the resistance effectively at the time when the ceramic material is inserted is formed on the surface of the mold that comes into contact with the ceramic material.
In the above-mentioned preparation method, it is possible to obtain a highly aesthetic fully ceramic artificial crown by including a step of coloring the surface by applying a surface-coloring material onto the surface of a fired article on which porcelain materials are baked followed by firing, and a step of lustering by applying a glazing powder onto the surface of the fired article obtained through the above step followed by firing. Here, the step of coloring the surface and the step of lustering are favorably effected by applying a kneaded product onto the surface of the fired article obtained in the step preceding said steps followed by firing, said ground product being obtained by grinding a staining powder or a glazing powder each comprising, as a chief sintering component, a glass material containing, on the basis of the oxides, 57 to 65% by weight of SiO2, 8 to 18% by weight of Al2O3, 15 to 25% by weight of B2O3, 0.1 to 2% by weight of ZnO, 3 to 7% by weight of Na2O and 2 to 8% by weight of Li2O with a kneading solution containing not less than 5% by weight of an ester compound having a boiling point of from 100 to 250xc2x0 C.
In the above preparation method, the solid lubricant is applied to the wax pattern by applying a suspension containing, for example, 0.1 to 30% by weight of a solid lubricant, 0.1 to 20% by weight of an organic binder and the remainder of an organic solvent, followed by drying.
When a crystallizable MgOxe2x80x94CaOxe2x80x94SiO2 glass material is used as a ceramic material, softened so as to possess a viscosity of from 102 to 109 poises and is put into a mold, there takes place the crystallization of the glass material during the molding of the ceramic core, making it possible to efficiently obtain a highly strong ceramic core.
In forming the mold, further, when there is used the crucible former having a pole member of which the diameter is widened downward being tapered at 0.005 to 0.120, it becomes easy to remove the crucible former from the assembly and, besides, the ceramic material being filled in the portion corresponding to the pole member of the former of the mold is not adversely affected even when it is being pushed by a plunger.
When the plunger is made of a ceramic material having a melting point or a decomposition temperature, whichever is lower, which is higher than a temperature of forming the ceramic artificial crown and having a thermal conductivity of not smaller than 0.1 (calxc2x7cmxe2x88x921xc2x7secxe2x88x921xc2x7xc2x0 C.xe2x88x921) or a coefficient of linear expansion of not larger than 4.0xc3x9710xe2x88x926 (xc2x0 C.xe2x88x921), there is no need of preheating the plunger at the time of molding the ceramic core, and the molding time can be shortened. When a solid lubricant such as boron nitride or the like is adhered on the surface of the plunger that comes into contact with the ceramic material, further, the plunger can be used again easily after the molding.
The present inventors have further discovered the fact that when a porcelain to which is added an inorganic crystalline powder having a particular refractive index is used, aesthetic property is improved compared to when a conventional porcelain is used.
That is, a second invention is concerned with a dental porcelain used as a body porcelain, an incisal porcelain or a translucent porcelain in the preparation of a ceramic artificial crown, and comprising:
100 parts by weight of a glass material containing, on the basis of the oxides, 57 to 65% by weight of SiO2, 8 to 18% by weight of Al2O3, 15 to 25% by weight of B2O3, 0.1 to 2% by weight of ZnO, 3 to 7% by weight of Na2O and 2 to 8% by weight of Li2O; and
0.1 to 10 parts by weight of an inorganic crystalline powder having a refractive index which is different from the refractive index of the glass material by 0.01 to 0.1, and having an average particle diameter of from 0.1 to 10 xcexcm.
When the above dental porcelain is baked, the color of the underlying ceramic core is blurred maintaining a suitable degree of transparent feeling, and a color tone close to that of a natural tooth can be realized.
Inclusive of the use of the dental porcelain of the present invention, the preparation method of the present invention can be preferably carried out by using a dedicated kit which constitutes the third and fourth inventions.
That is, the third invention is concerned with a kit used for the preparation of a ceramic artificial crown, which comprises:
a crucible former having a pole member formed on the central portion of a cylinder with bottom, said pole member having a recessed fitting portion at a central portion in the upper surface thereof to which a wax pattern is to be secured;
a ring that engages with the cylinder with bottom of said crucible former;
a backing member fitted to the inner surface of the ring;
a investment material filled between the crucible former and the ring;
a plunger for pushing the ceramic member filled in a portion corresponding to the pole member of the crucible former of the mold that is formed by curing the investment material, removing the crucible former and burning the wax pattern; and
a container for suspension to apply a solid lubricant onto the wax pattern or onto a portion of the plunger that comes into contact with the ceramics.
The fourth invention is concerned with a kit used for the preparation of a ceramic artificial crown while imparting color and luster, comprising:
a staining powder and a glazing powder each containing, as a sintering component and on the basis of the oxides, 57 to 65% by weight of SiO2, 8 to 18% by weight of Al2O3, 15 to 25% by weight of B2O3, 0.1 to 2% by weight of ZnO, 3 to 7% by weight of Na2O and 2 to 8% by weight of Li2O; and
a container for a kneading solution that contains not less than 5% by weight of an ester compound having a boiling point of from 100 to 250xc2x0 C.